Hmm. folks in Florida do gardening at 5:40am -- it's too hot to do it later in the day! But in Canada it does seem unusual.

I wake up with symptoms that suggest terror. It's either the apnea or low blood sugar. (I don't have nightmares.) After a few (or several) rounds of box breathing I can sleep again. But I've also did what you did and get up and putter around on a project.